1. Field of Invention
This invention relates to firearm systems having a barrel and particularly to smooth bore barrel system and ammunition that is achieving stability in flight by spinning the projectile.
2. Description of the Prior Art
The predominant group of the breech loaded contemporary weapons has helical rifled barrels. The purpose of rifling is, by having a close fit, to spin the projectile along the barrel and to give the projectile stability during the exterior ballistic, provided by gyroscopic effect. The rotation is around the main axis of the projectile and the barrel. Low rotation speed leads to less stability, very high rotation speed leads to, so called xe2x80x9cnose upxe2x80x9d-effect, otherwise the axis of the projectile crosses trajectory of exterior ballistic. Therefore the pitch of the rifling has to be carefully considered upon the range and the purpose of the projectile. The conventional projectile has a part of its surface (or jacket) that is slightly oversize or interference fit with regard to the bore diameter of the barrel of the weapon with which it is used. The surface (jacket) of the projectile is getting squeezed and engraved during the passage down the barrel of the weapon by the helical rifling grooves in the barrel. The projectile is spun by the rifling grooves to stabilize its flight as explained hereinafter. Considerable portion of the energy produced by the propellant is lost by the process of squeezing and engraving and by the dry friction between the projectile and rifled barrel along the acceleration. Engraving and friction not only consume the energy of the propellant but also transfer the kinetic energy once gained by hot propellant gases, again to heat. The friction and heat are serious problems especially for automatic or high caliber weapons, causing fast barrel erosion and loss of external ballistic propertiesxe2x80x94range and accuracy. Thermal enlargement of the bore barrel also leads to uncontrolled loss of pressure fit and less muzzle velocity affecting the same way exterior ballistic properties.
In order to reduce the negative effects of engraving and friction, several different approaches are established as state-of-the-art. Wide spread approach to reduce the dry friction is to put the projectile into a plastic cylindrical body (sabot) engaged with the projectile surface until both leave the muzzle thereby using friction plastic/metal instead of metal/metal and reducing the friction. Many patents used this approach so the patents cited herein: U.S. Pat. No. 3,847,082 issued to Feldmann F.; U.S. Pat. No. 3,769,912 to Friend W. H.; U.S. Pat. No. 4,063,511 to Bisping B. and they are cited here only as representative examples. A large variety of patents exploit similar approaches. Common and overwhelming drawbacks of introducing a sabot is the use of soft material preferably plastic, which decreases very fast its mechanical properties with increase of working temperature (especially in automatic weapons) and leads literally to smear the surface of the sabot along the barrel. Another disadvantage relates to the energy used to accelerate the sabot, which is not part of the projectile in flight, therefore the heavier the sabotxe2x80x94the bigger the loss of energy. One more disadvantage is that the projectile is always subcaliber compared to the full bore diameter with proportional reduction of the load.
Another approach is to use completely smooth bore barrel and a different means of providing the projectile with revolving momentum. One of themxe2x80x94U.S. Pat. No. 4,386,747 to Kuhl R. D. is using ammunition with means for self-generated revolving momentum.
A toroidal mass is disposed inside the projectile and attached and secured to the projectile by means of bi-convex spring or similar flexible structure so that the mass is setoff in oscillation upon the sudden acceleration due to the firing of the projectile. There are several drawbacks of this solution: the system is usable only for comparably big caliber weapon; a sufficient part of the weight and free volume of the projectile is used to accommodate the structure of toroidal mass, and bi-convex spring; an important part of the mass and volume of the projectile is engaged to provide revolving momentum; the relative density of the projectile is reduced.
Another direction is using only the smooth bore barrel to provide the conventional projectile with revolving momentum as in U.S. Pat. No. 4,841,657 to Mossberg A. I. The system is using axially rotating barrel moved by the force of expanded gases. The axially rotating barrel is engaged with the projectile surface whereby to impart rotary motion to the projectile. This system has to respond to controversial requirements. In order to provide revolving momentum to the projectile the barrel has to have a good grip with it. This defeats one of the main purposes of the smooth gun barrelxe2x80x94reducing the friction and friction-related erosion The increased grip will lead to increase of the temperature and thermal enlargement of the barrel. An enlarged barrel cannot provide a good grip thereby cannot provide a repeatable revolving momentum and will lead to significant lost of gas pressure.
Another disadvantage is that a big part of the propellant energy will be consumed for moving comparably big mass of the barrel, back, forward and around the axis with appropriate velocity. U.S. Pat. No. 4,176,487 issued to Manis J. R. teaches a system comprising a smooth bore barrel with annular grooves or pockets in the bore-walls which act as propellant gas pressure relief areas. When the projectile is fired, the helical notches on its rear part interact with the gas pressure relief areas or spaces of the bore, allowing the propellant gas to be expanded through the rear helical notches imparting a twist to the projectile. The system uses mutual interaction between specially designed bore barrel (referred as smooth bore barrel, despite a number of annular chambers along the barrel) and ammunition with rear helical notches. The drawback of this system is that the stress-point of each annular chamber reduces significantly the mechanical properties of the barrel. The difficulties of manufacturing and especially of cleaning such barrel from the products of propellant burning are another disadvantage. When in flight the helical notches will interact with air, imparting to the projectile an inverse directed twisting motion, therefore reducing the initial revolving momentum and abating the external ballistic properties.
There are two different parts of the barrel largely exposed to erosion. First one is breech part neighboring the cartridge nest, where the action of high temperature and high-pressure gases is combined with the process of engraving the projectile and dry friction. The second one is, before and at the muzzle, where the dry friction is combined with highest velocity of the projectile.
A very early notion of minimizing the erosion from the burning propellant and engraving is carried in the U.S. Pat. No. 37,193 to Alsop C. R. The patent suggests attaching a rifled section to the muzzle of smooth bore barrel thereby gaining a high speed and decreasing the erosion of hot gases at the breech section. The rifled section is engraving the projectile and giving to it revolving momentum. The patent admits that the rifling is imparting a considerable friction and transmitting substantial heat to the projectile, but those problems are said to be overcome by gained momentum of the projectile. The rifled section was suggested as a gradual reduction in diameter of the bore progressing away from the breech and into the rifled section. The length of the rifled section is proposed to be 2 to 3 inches. The rifled section has to be mounted to the main barrel by threaded connection with thread direction opposite to the rifling.
Despite the drawbacks of this concept, it was revitaized recently in U.S. Pat. No. H0001365 to Amspacker M. R. The concept reduces unacceptable erosion of the breech section. The gun barrel comprises a smooth bore breech section and a longer gain twist rifled muzzle section. The smooth bore breech section is said to be always less than one-fifth the total length of the gun barrel. The system claims to be accurate but the problem with erosion of the muzzle section seems to be even aggravated by higher speed of the projectile and the pitch of the rifling which increases from its beginning to the muzzle end.
It is known system utilizing a smooth bore barrel fitted with a short rifled insert near the breech (U.S. Pat. No. 4,712,465 to Macdonald Kenneth A. B.). A projectile comprising perforated skirt and driving band about the base of the skirt is loaded into the gun barrel so that the driving band just engages the rifled insert and the warhead portion of the projectile extends into the smooth bore portion of the barrel. Upon firing of a breech charge, gases from the breech charge are ducted to the space between the thin sidewalls of the projectile and the smooth central bore, thereby establishing a gas bearing. The gas from the bearing provides lateral support to the projectile and lubricates the projectile. Drawbacks of that system are the presence of the driving band, which has to be durable enough to be engraved and to transfer the rotation impulse to the projectile. Same driving band has to be soft enough to get squeezed into specially formed annular groove thereby to form a cylindrical body with the entire projectile. Again part of the propellant energy is consumed to engrave and to fabricate in-situ with all heat related consequences. The system is designed to spin comparably big caliber projectiles or fin stabilized rockets.
Another system using combination of a rifled bore section at the breech and a smooth bore section at the muzzle end is proposed in U.S. Pat. No. 4,660,312 to A""Costa A. The diameter of the smooth bore section is greater than the diameter of the bore of the rifled bore section and smaller than the diameter of the spiral-rifled groove. The system therefore is vulnerable to have gas pressure losses along the grooves of the projectile during the acceleration or to have a spin momentum losses in the smooth bore section because the fit is too tight. The system proposes a way to decrease those drawbacks by having a compromised smooth bore diameter. The friction thereof is still a persisting problem, but instead of engraving grooves, the smooth bore is squeezing the projectile to get better gas fit. This fact can lead to big, if not to entire, lost of revolving momentum.
It will readily be appreciated by those skilled in the art, that none of the approaches used herein is providing a complete solution of the problems associated with rifled bore barrel Some solutions are more or less applicable to a certain class and caliber systems, and only few of them correspond to the requirements of automatic firing weapons.
General objective of the present invention is to overcome the drawbacks of the prior art discussed heretofore. Dry friction and heat generation along the barrel will be reduced drastically thereby reducing the erosion in the breech part and the muzzle part of the bore, which are more vulnerable to wearing.
Another objective of the present invention is to reduce the amount of propellant used to give appropriate impulse and velocity to the projectile. Proportionally will be reduced the revolving impulse stabilizing the projectile in fight. This objective is aiming to reduce the weight of the ammunition needed for the same mission.
Consecutively another objective of the present invention is to allow achievement of substantially higher muzzle velocity therefore substantially higher range of fire.
Another objective of the present invention is to increase the mass fraction ratio between ordnance payload mass to structural mass of the projectile thereby increasing the effectiveness of the bigger caliber projectile.
The present invention uses two different aspects in combination or solely to achieve the set objectives heretofore. According to the first aspect of the present invention the firearm encompasses a smooth bore barrel having a nest for the cartridge in the breech part. This nest contains the cartridge having its front section facing the muzzle and having inner diameter substantially the same as the diameter of the bore of the barrel. This section of the cartridge has a rifled inner surface with grooves and lends representing itself a short rifled barrel As the cartridge case is assumed to be disposable this rifled section could be referred also as disposable rifled barrel. The diameter of the grooved part of the cartridge is substantially the same and slightly smaller than the diameter of the smooth bore. The diameter determined by the lands is smaller with a fraction representing twice the depth of the grooves. The ratio between the two diameters is substantially the same as this in the rifled bore barrel of the same caliber. The pitch of the helically-rifled section is substantially higher than the regular one of same caliber conventional barrel In this rifled section of the cartridge is engaged relatively long portion (up to 98%) of the cylindrical part of the projectile. This engaged cylindrical portion has outer surface with grooves and lands congruently matching those of the rifled section of the cartridge. A thin layer of dry or paste with small coefficient of friction, based on graphite or molybdenum sulfide, is used to hermetically seal the projectile into the cartridge. A non-rifled cylindrical portion of the projectile, representing 2 to 10% of the cylindrical length, but not limited to this range, is extended from the front end of the cartridge into the basic smooth bore barrel This non-rifled cylindrical portion taper with smooth transition to streamline ogival front part of the projectile. The non-rifled portion has a sliding plunger fit to the bore surface. The rear part of the projectile facing the breech has preferably ogival shape thereby to provide the projectile with better fairing shape.
In particular case explained hereinafter, rifled grooves could be parallel to the axis of the projectile, therefore no pitch is applied to the grooved (rifled) surface.
According to the first aspect of the present invention there are two distinguishable phases of the interior ballistic. First of those phases includes the moment of ignition and initial move of the projectile along the short rifled barrel section of the cartridge. The second phase starts when the projectile leaves the rifled section and moves down the barrel. When the propellant is ignited, the hot gases start to expand and develop an axial force. This axial force moves forward the projectile when the helically engaged grooves revolve the projectile providing a spin enough to keep the stability by gyroscopic effect along the acceleration in the barrel to the muzzle and further during the exterior ballistic. The expanding gases act on the entire rear surface of the projectile push and revolve the projectile out of the rifled section of the cartridge. Immediately after the projectile leaves rifled section, the grooves on its surface become open to the expanding gases, which are ducted in them, providing strong lateral support over all grooved area. The front cylindrical portion of the projectile, having a sliding fit with the bore, insures the gases from escaping and decreasing the pressure. The gases in the grooves and the sliding fitted annular space provide a gas lubrication effect as well as enduring effect on the projectile walls during entire phase of acceleration after leaving the cartridge. Those effects of gas lubrication and lateral support make possible to avoid dry friction, hit generation and to increase the ratio between the masses of the payload and the structure of the projectile.
The presented heretofore aspect of the invention is convenient solution for small, medium and comparably high caliber systems or for automatic fire of the small and medium caliber arms. There is no any technological complication""s using the present invention. Manufacturing a smooth bore barrel is substantially easier compare to conventional rifling. Manufacturing the ammunition round includes the same main procedures regularly applied for small and medium caliber rounds involving rolling tools particularly shaped.
During the first phase of interior ballistic, the defined short rifled section of the cartridge is exposed to high temperature and friction instead of the corresponding part of the main barrel, therefore preventing it from erosion. During the second phase-acceleration, the friction between the barrel walls and the projectile""s outer surface is minimal, the projectile uses all the pressure force for acceleration to higher level, therefore minimizing erosion of the barrel. The improved efficiency of the propellant could be used different ways:
To increase the muzzle velocity and the range of the fire. (The range increases with square of the muzzle velocity improving the effectiveness of the weapon);
To increase the total mass of the projectile at the same velocity;
To decrease the total mass of the propellant used for acceleration of the same mass of the projectile keeping previously established ballistic properties;
To have a combination of all of the above-mentioned benefits aiming to achieve higher efficiency of the weapon system-more rounds with longer range per same weight at sufficiently higher barrel fife.
The use of the first aspect of the present invention has technical consequences which influent the entire system. The short rifled bore barrel, part of the cartridge case, is exposed not only to thermal, thermo-chemical and mechanical erosion, but also to the revolving recoil impulse-torque. Part of this revolving impulse-torque is transferred by friction of slightly expanded cartridge neck (short rifled barrel) directly to the walls of the breech Another part of the torque is transferred by the structure of the cartridge to its rear wall, which has means to engage the breech part of the weapon. The rear part of the cartridge has a star-shaped wreath of small trangle prisms or flukes, which are engaged congruently with the opposite breechblock part, shaped the same way. The main axial recoil impulse is pressing hardly on the rear pattern, preventing the cartridge case from twisting. To receive sufficient revolving impulse at the very beginning of acceleration, the slope or pitch of the rifling must be more severe. The more severe rifling can lead to reinforcement of the short rifled part of the cartridge and its walls therefore to increase the weight of the cartridge, especially for medium and bigger caliber weapon.
Different approach is used to avoid the cartridge reinforcement and to improve further the performance and versatility of the system, resulting in another aspect of the present invention.
The second aspect of the present invention uses different approach to avoid reinforcement of the cartridge walls and to improve further the performance and versatility of the system. It is related to the second distinguished phase of interior ballistic starting in the moment when the projectile leaves the end of the short rifled barrel. According to this aspect, the projectile gains additional revolving impulse traveling down the smooth bore barrel.
At least a couple of substantially opposite longitudinal grooves extends into narrow channels through the non-grooved cylindrical portion of the projectile. This portion is preferably 5 to 10% of the entire cylindrical length. Those narrow channels change its direction to the opposite of the direction of the revolving impulse and gradually enlarge to the front ogival shaped part of the projectile therefore forming jet nozzles within the space secluded between the barrel wall and the channel. The narrow part of the channels forms the throat enlarging to the nozzle. When hot gases ducted into the grove reach the throat and the nozzle they produce an effect of a jet. Each nozzle has to have direction opposite to the revolving impulse. A small portion (0.1 to 5%) of the high-temperature and high-pressured gases goes throughout the groove, throat and leaves the nozzle, providing jet forces and revolving impulse to the projectile.
Depending on the caliber of the projectile, more than one couple of grooves could be transformed to jet nozzles therefore bigger part of the revolving impulse would be generated by jet forces rather than by the short rifled barrel. The proportion between the parts of the revolving impulse gained, according to both aspects of the present invention, depends on the purpose, caliber and other engineering considerations. When the grooves are parallel to the axis, there is no revolving impulse generated according to the first aspect, therefore only the second aspect is to be applied. In this case at least one couple of opposite grooves is necessary to be transformed to jets. For big caliber projectiles the gain of revolving impulse upon the second aspect of the present invention can reach 100% and all grooves can be transferred into jets. As far as all of the grooves, according to first and second aspects of the present invention, are insulated from direct friction with the barrel by dry lubricating layer, groove""s bottom surface could be used for identification purposes. Traced shallow lines similar to one used for barcode could be imposed on the bottom of the groove during manufacturing/assembly process. This will allow batch identification and further backtracking of the used ammunition and its linking to the customer /in this case customer ID would be required,
The use of the second aspect of the present invention leads to reduction of torque recoil and better lubrication of sliding fitted projectile and barrel surfaces. It is clear to one skilled in the art, that each one of both aspects can be used separately or their effects can be combined togetherxe2x80x94each one contributing part of the finally gained revolving impulse.